Preparation of film casting surfaces



Patenteol Dec. 23, 1952 Qrange, N. J assignors to qelanese Corporation of America, New York, 15L Y., a corporation of Delaware 7 NoDrawing. Application-February l, 1950,

Serial No. 1415846 (01.. awn .5)

7 Claims. 1

This invention relates tofilm casting surfaces and relates more particularly to anovelprooess for preparing film casting surfaces .that .Willproduce films free from defects.

One of the processes heretofore employed; for the productionof films involves the flowing of dope containing a film-formingmaterial, ontothe surface of a casting membercornprising a rotat,- ing, cylindrical casting drum having a diameter of from 10 to 18 feet, or more, and, after the dope has set, stripping the films from the drum. To obtain films free from defects, ithas-been the practice to provide the casting drum with a smooth, glossy casting surface by plating chromium, nickel or other corrosion-resistant metal thereon. The preliminary surface treatmentof the casting drum to obtain a smooth and blemishfree deposit by platingand the plating operation itself are not only verycumbersome, but also extremely expensive and require a .considerable period of time. Often the surfaceof the casting drum isdamaged byscratchesand other marks shortly after the final plating. and must. then be completely refinished.

To overcome the foregoing difficulties, it .has been proposed to substitute for the plating on the casting drum a layer of gelatin or a cellulose ester coating. However, the application of these materials has not proved practical. the case p of gelatin, the joining. of-the ends of the layer is extremely difiicult, as will be understood-by those familiar with the'art. As,-for thefcellulose ester coating, the swelling, andparticularlythe uneven swelling, of thecellulose ester duringathe casting of films has proved adeterren'tgto its use.

In anotherprior process for the production of films, the dopecontaining the film forming material is flowed onto the surface of al'cast'ing member comprising an endless belt disposed'in a horizontal plane and trained overa, number of pulleys. It has been proposed to provide this lend itself .to .the jqq enon. fiil fcasti igsurfaces on a casting drum. If a solution containing adeeesterifyingagent is ,ad acentthe top .of va casting idruin coveredwitli a "cellulose derivative coating, theisolutioni lillru n down from the top of the d unilin both directionsgand .will produce streaks; and other -nonuniformities in the surface .of the-cellulose derivative I coating.

9 ml Qn-theother hand, a disassembling of the'casting unit would be required to apply the solution tozthe' bottom of'casting drum.

Even" in the case of a casting belt, longitudinal streaks are frequently produced during the treatment of acellulosederivative coating with a solution containing a de-esterifying agent owing to the uneven application and mixing-of the solution an variei c c th belt- A great el' ski l is also required in stoppin and starting the application of the solution to avoid the produc- .tion of very distinct marks on the film casting surface, which marks will be reproduced on the films cast thereon. lvioreover, thetreatmentof the cellulose derivative coating with a solution containing ade-esterifying agent necessitatesan extendedwashing'to removefrom the coating the excess of de-esterifying agent, during which washing ther isa tendency to forrn fiag marks on the coating which will be reproduced as defects in the films.

ployed for thispurpose and which will be especiallysiinple'and efiioient in operation.

Aufurther object of this invention is toprovide a novel process for preparing film casting surfaces that will produce films free from defects.

Another object of this invention is the provision of a novel process for preparing on a casting drum film casting surfaces that will produce films free from defects.

Other objectsof this invention will be apparent from the following detailed description and claims.

According to the present invention, a film oasting surface is prepared bycovering the periphery of a castingdrum, belt and the like with a celluloselderivative coatin having a smooth, glossy surface, flowing a viscous dope containinga filmforming-material and a reagent-capable of chemically altering the cellulose derivative ontothe cellulose derivative coating to form a film, and

agent-containing film from the cellulose derivative coating to expose the film casting surface which has been rendered solvent insoluble while glossy finish. This film ventional manner for the production of;films. The process of the present invention may be car- 'riied'out without modifying the equipment presently employed for the production of films by using the standard film-casting hopper for applying both the cellulose derivative coating and the reagent-containing dope to the casting member.

The reagent-containing dope may be applied on the cellulose derivative coating to form a film having one or a plurality of layers extending over the entire surface of the cellulose derivative coating. After the reagent has effected the desired change in the cellulose derivative, the reagent-containing film is stripped off, exposing the film-casting surface. Alternatively, the reagent-containin dope maybe applied to the cellulose derivative coating as a single film which is stripped from the coating when it reaches the normal stripping point. In this event, the reagent-containing dope is applied to the cellulose derivative coating for a period long enough to obtain the desired change in the cellulose derivative.

As indicated, this invention may be employed for the preparation of a film-casting surface on a casting drum as well as on a casting belt. Owing to the viscosity and to the setting of the reagent-containing dope, the formation of streaks and other defects on the film-casting surface is eliminated. In addition, since it is no longer necessary to apply an excess of reagent to the cellulose derivative coating, the washing step hitherto employed for the removal of excess reagent may be dispensed with. The process of this invention requires much less time than the processes hitherto employed and, what is more important, leads to a greater and a more uniform depth of reaction. As a result of the greater depth of reaction, the film-casting surface is more durable since dust particles and fine scratches do not extend through the altered upper layers of the cellulose derivative coating and do not permit the access of solvent to the unmodified and solvent sensitive lower layers of the cellulose derivative coating. Blemishes in the surface of the coating, if they are not too deep, can, therefore, even be repaired without fear of reaching the solvent sensitive lower layer. By controlling the nature of the solvent or solvent mixture and quantity of reagent in the reagentcontaining dope so that the solvent or solvent mixture evaporates and/or the reagent is exhausted before reaching too great a depth in the cellulose derivative coating, the reagent-containing film may be left in place to act as a protective layer until just prior to placing the casting unit in operation.

The cellulose derivative coatings employed in carrying out this invention may have a basis of a cellulose ester or mixed ester such as, for example, cellulose acetate, cellulose propionate, ce1lulose butyrate, cellulose-acetate propionate and cellulose acetate butyrate.

The cellulose derivative coatings may be chemically altered by de-esterification with any suitable reagents, e. g. alkaline materials such as potassium hydroxide, potassium or sodium alcoholates, amines or quaternary ammonium hydroxide, for example. The viscous dope into which the reagents are incorporated may contain any suitable film-forming material that will not react with the reagents. For example, the dope may be prepared with ethyl cellulose, carboxymethyl cellulose, methyl cellulose or an alkali soluble copolymer of styrene and maleic anhydride designated as Lustrex X-8l0. The dope dispersed, and which does not attack the cellulose derivative coating. Th solvent or solvent mixture may have a swelling action on the celluose derivative coating and aid the difiusion of the reagent into the coating and thereby help in the de-esterification of the cellulose derivative.

The dope may be applied to the cellulose derivative coating at room temperature or at an elevated temperature and may be made up with any desired concentration of reagent. The time of treatment will depend upon the character of the cellulose derivative coating, the temperature of the dope and the concentration of the reagent therein and may be varied to alter chemically the cellulose derivative coating to any desired depth. The following examples are given to illustrate this invention further.

Example I The process of Example I is repeated, using a dope containing 15% by weight of ethyl cellulose and 0.4% by weight of sodium hydroxide in methanol. After stripping the ethyl cellulose film, the cellulose acetate coating is found to be de-esterified to a depth of 0.0003 inch.

Example III The process of Example I is repeated, using a dope containing 15% by weight of Lustrex X-810 in water together with sufficient potassium hydroxide to dissolve the Lustrex X-810 and an excess of 1.5% by Weight. After stripping the Lustrex X-810 film, th cellulose acetate casting is found to be de-esterified to a depth of 0.001 inch.

Example IV The process of Example I is repeated, using a dope containing 5% by weight of carboxy methyl cellulose in water together with 0.5% by weight of potassium hydroxide. After stripping the carboxy methyl cellulose film, the cellulose acetate coating is found to be de-esterified to a depth of 0.001 inch.

It is to be understood that the foregoing detailed description is given merely by Way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by Letters Patent is:

1. In a process for the preparation of film casting surfaces, the steps which comprise covering the surface of av casting member with a cellulose ester coating, and flowing a viscous dope containing a film-forming material and a reagent inert to said film-forming material and capable of de-esterifying the cellulose ester onto the-surface of said cellulose ester to de-esterify the surface of said cellulose ester coating.

2. In a process for the preparation of filmcasting surfaces for the reception of a solution of a film-forming composition in a volatile solvent therefor, the steps which comprise covering the surface of a casting member with a cellulose ester coating, flowing a viscous dope containing a film-forming material and a reagent inert to said film-forming material and capable of deesterifying the cellulose ester onto the surface of said cellulose ester coating to de-esterify the surface of said cellulose ester coating, and stripping the reagent-containing film from the cellulose ester coating to expose the film-casting surface.

3. In a process for the preparation of filmcasting surfaces for the reception of a solution of a film-forming composition in a volatile solvent therefor, the steps which comprise covering the surface of a casting drum with a cellulose ester coating, flowing a viscous dope containing a film-forming material and a reagent inert to said film-forming material and capable of deesterifying the cellulose ester onto the surface of said cellulose ester coating to de-esterify the surface of said cellulose ester coating, and stripping the reagent-containing film from the cellulose ester coating to expose the film-casting surface.

4. In a process for the preparation of filmcasting surfaces, the steps which comprise covering the surface of a casting drum with a cellulose ester casting, flowing several superimposed layers of a viscous dope containing a film-forming material and an alkaline agent inert to said filmforming material and capable of de-esterifying the cellulose ester onto the entire surface of the cellulose ester coating to de-esterify the surface of said cellulose ester coating, and stripping the film containing the alkaline agent from the cellulose ester coating to expose the film-casting surface.

5. In a process for the preparation of filmcasting surfaces, the steps which comprise covering the surface of a casting member with a cellulose acetate coating, and flowing a viscous dope containing a film-forming material and a reagent inert to said film-forming material and capable of de-esterifying the cellulose acetate onto the surface of said cellulose acetate coating to de-esterify the surface of said cellulose acetate coating.

6. In a process for the preparation of filmcasting surfaces, the steps which comprise covering the surface of a casting member with a cellulose acetate coating, flowing a viscous dope containing a film-forming material and an alkaline agent inert to said film-forming material and. capable of de-esterifying the cellulose acetate onto the surface of the cellulose acetate coating to de-esterify the surface of said cellulose acetate coating, and stripping the film containing the alkaline agent from the cellulose acetate coating to expose the film-casting surface.

7. In a process for the preparation of filmcasting surfaces, the steps which comprise covering the surface of a casting drum with a cellulose acetate coating, flowing several superimposed layers of a viscous dope containing a filmforming material and an alkaline agent inert to said film-forming material and capable of deesterifying the cellulose acetate onto the entire surface of the cellulose acetate coating to deesterify the surface of said cellulose acetate coating, and stripping the film containing the alkaline agent from the cellulose acetate coating to expose the film-casting surface.

LEOPOLD ECKLER. WILLIAM P. MOELLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,175,169 Muller-Naegeli Mar. 14, 1916 1,988,550 Gladhorn et al. Jan. 22, 1935 2,353,717 Francis et al July 18, 1944 

1. IN A PROCESS FOR THE PREPARATION OF FILMCASTING SURFACES, THE STEPS WHICH COMPRISES COVERING THE SURFACE OF A CASTING MEMBER WITH A CELLULOSE ESTER COATING, AND FLOWING A VISCOUS DROP CONTAINING A FILM-FORMING MATERIAL AND A REAGENT INERT TO SAID FILM-FORMING MATERIAL AND CAPABLE OF DE-ESTERIFYING THE CELLULOSE ESTER ONTO THE SURFACE OF SAID CELLULOSE ESTER TO DE-ESTERIFY THE SURFACE OF SAID CELLULOSE ESTER COATING. 